If you have ever shot with a digital camera in dark conditions, you understand how devastating video noise can be. It can take a beautiful performance and render it useless, being only viewable as dancing colored dots. While many things can be done to reduce noise while the material is being shot such as additional lights, black balancing, etc, there will always be a few times when some noise reduction is post is a necessity.
- Focus on reducing "chroma \ color" noise before "luminance" noise to maintain detail.
- Our eyes are much more sensitive to luminance detail than chroma or color detail, so overdoing noise reduction on the luminance channel tends to result in a overly smooth "plastic" looking image.
- If possible, apply noise reduction first, prior to any color correction or other effects.
- While there are exceptions, I generally recommend applying any noise reduction prior to doing any color correction or effects, so you have a "clean" source image. The benefit is the NR helps during color and effects, especially if keying is involved . The downside is noise reduction is a resource hog and can require a fast computer to get real-time playback. Caching can help, but it still slows the process down, especially with high resolution media.
- Adjust Temporal before Spatial
- Although the best noise reduction is usually accomplished using a combination of both methods, temporal noise reduction usually retains more detail, at the cost of being slower and using more video RAM. Temporal NR works by comparing details between a set number of frames, and eliminating per-frame changes, such as video noise. Resolve Studio's built-in NR allows up to 2 frames (forward and backward), while 3rd-party effects like NeatVideo support up to 5 frames, if your hardware can handle it. Spatial NR looks at details in nearby pixels to figure out what is "noise" and averages certain areas of pixels. While useful in small amounts, it can dramatically reduce the "sharpness" and results in a artificial "plastic" look to the image if overused, but faster than temporal.
- Apply a fine level of noise or "film grain" to dither the image and eliminate banding
- After any noise reduction, the image is likely to look a little "off", even if a very light level of noise reduction was used. You may even see some banding in areas like skies and shadow areas, especially if the source was heavily compressed such as H.264 \ AVCHD. However, we can add some "life" back to the image in several ways: mixing back a slight level of the original noise, adding noise via an effect, or overlaying synthetic or scanned film grain over the image, reduced in opacity until it is barely visible, usually between 15% and 45%. The intended effect is dithering of the image, which blends together areas that were banding and adds some texture and localized contrast back to skin and other areas with fine details. You can add more grain for creative effect, but only a very small amount of noise \ grain is required for this technique to be effective. For HQ grain, I highly recommend RGrain (for synthetic grain ideal for invisible dithering) and CineGrain (for more filmic grain scanned from real film). For the budget conscious, I also created free film grain that you can download here to experiment with.
- Less is More
- When even my favorite plug-in includes an Auto button, I feel it is important to always remember that ANY noise reduction is technically "damaging" the footage and the less we do, the better. Before blindly dragging a filter to every clip and using "auto", really zoom in and evaluate if noise reduction is necessary on each clip. If it is, tune it so you are doing the least amount of "damage" to your image with the best results. I guarantee you can do better than ANY auto or "one click" button with a few seconds of customization.
While noise reduction and texture management is a huge subject that can't be completely covered in a single blog post, these are a few tips I find hugely useful when working with noise reduction in general. If you have any additional tips or questions, please post a comment, send me a tweet, or post to our facebook page.